Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$111.49	4.516%	$116.5249	$116.52	$116.50	$116.50
Purchase #2	$56.72	6.709%	$60.5253	$60.53	$60.55	$60.50
Purchase #3	$11.88	13.613%	$13.4972	$13.50	$13.50	$13.50
Purchase #4	$237.53	13.599%	$269.8317	$269.83	$269.85	$269.80
Purchase #5	$246.72	12.434%	$277.3972	$277.40	$277.40	$277.40
Purchase #6	$170.25	5.492%	$179.6001	$179.60	$179.60	$179.60
Purchase #7	$218.72	7.455%	$235.0256	$235.03	$235.05	$235.00
7 purchase totals =	$1,053.31		$1,152.4020	$1,152.41	$1,152.45	$1,152.30